Roots: Heist movies. The Doctor and Lucie's TARDIS robbery plan owes a great deal to the Trojan Horse. Karen mentions 'Butch Cassidy stuff' (specifically their train robbing episodes), the Headhunter uses the phrase 'Elvis Presley' as a post-hypnotic trigger. Lucie introduces herself as Ms Palmer-Tomkinson (after Tara Parker-Tomkinson) The Doctor mentions August Strindberg, the original 'Napoleon of Crime' Adam Worth and fictional 'gentleman thief' A.J. Raffles. Some music cues (especially the theme) come from the Cosmic Hobo series The Scarifyers. One of Tardelli's works is an homage to Botticelli's Mars and Venus

Double Entendres: We're showing our age, perhaps, but we can't hear the phrase 'black diamond' without imagining the story as some sort of weird heist involving an old Mitsubishi video recorder.

Continuity: Claudio Tardelli was a 17th century Italian artist, made obscure because the Doctor has done his level best to keep him that way. Tardelli apparently never did miniatures - although this seems to be a falsehood. Exiled to Earth (the Headhunter say this is now complete), Tardelli is an alien from the planet Parrimor. He designed the Black Diamond as an emergency bolt-hole and escaped to it when his situation in Florence became untenable. It is a masterpiece of compression and contains a small self-sustaining Universe fewer than three light-years across, which he rules. Under the Doctor's threat, Tardelli is able to perform a fifth-dimensional jump, removing the pocket universe to a space between universes and, ultimately, out of the artist's influence.

The Diamond's Guardian is a twelve-foot tall stone statue, a silicon-based life form designed to learn from past attacks and respond accordingly (the Headhunter's weapon temporarily scrambles its neural pathways only once.)

The Emperor Vassilar-G of Ralta's taste is notoriously fickle. It's rumoured that when he gets bored of his artists he goes out onto his balcony and eats them in front of his subjects.

The Headhunter is after Tardelli as a designer for one of her clients, a Russian industruialist by the name of Yashin. Yashin wishes to break the Black Diamond down and use it as a power soure to keep him ahead of his competitors (she knows, meanwhile, that he will be murdered by his own workers in 1905.) She explains that the phrase "I obey" is a default setting on most mind-probes. Her ship has an ion-jet engine.

Karen used to work in Elisabeth Duke's. She is angry with Lucie for apparently leaving her for dead during the Cyberman involvement with Hulbert Logistics (see: Links)

Lucie has never been to Russia before (it's good to know she's conscientious about her visit to Uzbekistan)

The Doctor admits that he came to Sweden especially to ride the electric railway and is quite interested in the new play by Strindberg. He uses his sonic screwdriver to analyse the molecular structure of the black diamond and creates a short-range feedback loop generator, which creates a false impression of the surroundings of a target individual, enabling the Doctor to steal a possession from them unawares.

Untelevised Adventures: The Doctor implies that he knew Robin Hood; he has met Tardelli before (or will meet him again) in another incarnation. They first crossed paths in Rome and the Doctor discovered that Tardelli's works warped t6he fabric of reality to the extent of changing those people who examined them. Realising Tardelli wasn't human, and was attempting to gain influence over the Pope, the Doctor had him discredited; but Tardelli escaped Florence, leaving the Doctor to destroy any samples of his work he could find.

Another Robson Reliant, with some of the best double-act work yet from the Doctor and Lucie, and their opposites the Headhunter and Karen. Possibly there's not enough of a sense of threat or danger to the regulars to carry the drama along, but the farcical heist scenes certainly do, and by the time Christopher Benjamin's coldly amoral Tardelli emerges, everything is well in place for an indulgent re-listen.